Shear modulus and internal friction of polymethyl methacrylate and polyethyl methacrylate between 4.2 and 100°K

Local free volume and structural relaxation studied with photoisomerization of azobenzene and persistent spectral hole burning in poly(alkyl methacrylate)s at low temperatures

“…Except PMMA, the order of final cis fraction agrees well with that of o-Ps lifetime. As mentioned above, it has been reported that the ester methyl group rotation in PMMA begins at 4 K. 23 The larger value of the final cis fraction for PMMA than the expected value from the o-Ps lifetime may be due to the effect of the ester methyl group rotation. The ester methyl group rotation in PMMA might assist the photoisomerization of azobenzene even at 4 K, as already discussed.…”

“…23 However, it was also shown that the rotation of the ester methyl group around the COO bond (␦relaxation in PMMA) starting below 20 K did not influence the hole-width increase in a 20K-cycling experiment for PMMA, 19 probably due to the good symmetry of the ester methyl group. The difference in the results of photoisomerization of azobenzene with a rather high final cis fraction at 4 K and PSHB measurements with narrow hole width at 4 K in PMMA could also be caused by an excited-state azobenzene molecule "pushing" its surroundings during its isomerization, leading to easier occurrence of photoisomerization, in cooperation with the fluctuating surroundings.…”

Temperature dependence of ESR spectra of methyl methacrylate radicals from 77 K to 300 K

“…The reaction rates can be monitored by means of the viscosity of the solid medium as the temperature is slowly changed. It was reported in earlier research that the rotation of the ester methyl group in PMMA occurs below 4.2 K. 35 The rotation of the main chain methyl group occurs over 100 K and was observed by many experimental methods, which include the NMR second moment absorption line m e a~u r e m e n t .~~ Thus, these results are consistent with our observation that the radical reaction rate changes rapidly when the structure and the symmetry of the surrounding matrix changes. The measured value of the NMR second moment absorption line measurement showed that, above 130 K, the second moment decreases and reaches a constant value a t 250 K, which is comparable with the calculated value for the case of hindered rotation of both methyl groups.…”

Dynamic mechanical behavior of some high polymers at temperatures from 6°K.: Polyethylene, nylon 66, polypropylene, poly(vinyl chloride), poly‐(d,l‐propylene oxide), polybutene‐1, poly(4‐methyl‐pentene‐1), poly(methyl methacrylate), poly(ethyl methacrylate), poly‐4‐methylpentene‐1 and poly(isobutyl methacrylate)

“…in PEMA has been attributed to configurational rearrangements involving the side chain ester ethyl groups. 6 In view of the absence of this peak for PMMA, such an assignment appears correct. I n addition, a T I minimum attributed to ethyl group motion was found at 143'K.…”